At present, oil and gas extraction and geological and geothermal probing are carried out by drilling rigs, where disintegration of the rock is performed by rotating drilling heads. The drilling heads are secured at the end of assemblies of connected basic pipes, and the drilling heads are rotated at the surface by driving units. The disintegrated rock is transported to the surface by a special liquid, circulating in the piping and in the borehole formed by the drilling heads. In the past, turbine driving units have been used near the drilling head wherein the energy is supplied from the surface by an aqueous carrier, which also flushes the crushed rock from the system. Energy has also been supplied by electrical cable. Nevertheless, the transport of the disintegrated rock is performed in both systems by classical method—using a viscous circulating liquid.
Especially in the last decade, new methods of more efficient performing of rock disintegration and of its transport to the surface have been searched for.
The study of MIT (USA) “The Future of Geothermal Energy”—Impact of Enhanced Geothermal Systems (EGS) on the United States in the 21st Century 2006-points to the crucial importance of developing economically efficient technology of drilling deep geothermal boreholes. The price of the borehole increases exponentially with depth when using present drilling technologies. Therefore, there exists an urgent need to find drilling technology for which the price of the borehole would increase approximately linearly with the borehole depth.
A coauthor of the above study, Jefferson Tester, characterizes in his presentation requirements for a new, quick, and ultradeep drilling technology as follows:                the drilling price increases linearly with the depth        neutrally flowing drilling axis        ability to drill vertically or at an angle to depths of over 20 km        ability to drill large diameters up to five times larger than at the surface        casing is formed inside the borehole.        
Over twenty innovative technologies of drilling in geological formations of various sophistication are known.
From the state of the art we shall describe only the most promising technologies or those that have already been examined.
Overview of Present Technologies:
The technologies may be evaluated also according to such properties as specific energy necessary for an extracted cubic centimeter, the maximum possible performance at the borehole bottom, and maximum available drilling speed.
From this point of view, the most important role is played by mechanical principles such as electro-spark discharges in water and water beam cutting.
Among available solutions, which are not yet completely viable for deep geothermal conditions, there may be included the following examples:                technologies of drilling by means of rotary casing (TESCO CASING DRILLING), which eliminates one system of pipes but does not alleviate the substantial negatives of mechanical drilling; and        technology of coil composite piping with electric power transmission line for driving of drilling at the bottom of the borehole (HALLIBURTON/STATOIL-ANACONDA), which eliminates the rotating element of the drilling pipe for transmission of mechanical energy but does not solve the issue of flushing the crushed rock from the system.        
Considerable progress in drilling technology is represented by the U.S. Pat. No. 5,771,984 of the authors Jefferson Tester et al., titled “Continuous Drilling of Vertical Boreholes by Thermal Processes: Rock Spallation And Fusion”, where the energy to power the drilling rig at the bottom is delivered by power water, which flushes the borehole, drives the turbine, and produces electric energy for the actual process of drilling by thermal spallation or fusion of the rock. The invention of U.S. Pat. No. 5,771,984 is also the basis for the subject matter of the firm Potter Drilling LLC, the technologies of which are already in the state of prototype testing.
Related technologies are described in the U.S. Pat. No. 5,107,936 titled “Rock Melting Excavation Process”. The author Werner Foppe describes a process by rock fusion on the circumference of the borehole, pressing the melt into the core and breaking of the core. The same author describes in the U.S. Pat. No. 6,591,920 fusion of the rock and its pressing into the surrounding rock.
Cutting the rock by a plasma beam is described in the U.S. Pat. No. 3,788,703 by Thorpe. Nevertheless, it does not solve removal of the crushed rock.
At the University in Tel Aviv, the authors Jerby et al.: JOURNAL OF APPLIED PHYSICS 97 (2004) solve the process of rock spallation by local overheating using microwaves.
The largest group of patents covers technology of cutting the rock by a water beam.
Described are variants of different modifications, for example utilization of cavitation, turbulent processes, combinations with other mechanical principles and the like. For example the U.S. Pat. No. 5,291,957 describes the process of using a water beam in combination with a turbulent and mechanical process.
In the last decade, intensive research of utilization of high-energy laser beams for rock disintegration is in progress. It concerns especially the conversion of military devices for disintegrating rock. The laser energy is used for the process of thermal spallation, fusion and evaporation of the rock.
The patent of Japanese authors Kobayashi et al., U.S. Pat. No. 6,870,128 titled “Laser Boring Method And System”, describes laser drilling, where the light beam is fed from the surface through optical cable to the borehole bottom. This system evaporates the rock, which requires high consumption of energy.
The authors Zhiyue Xu et al. describe in the paper LASER SPALLATION OF ROCKS FOR OIL WELL DRILLING, published in the Proceedings of the 23rd International Congress on Applications of Lasers and Electro-Optics 2004, a method of thermal spallation, which is energetically more favorable, but removal of the crushed material is performed by classical flushing.
Methods of using electric discharge are based on long-term experience in other application areas. The method described in the U.S. Pat. No. 5,425,570 of the author G. Wilkinson is based on a combination of electric discharge with subsequent explosion of a small amount of an explosive or of an induced aluthermic process.
U.S. Pat. No. 4,741,405 and U.S. Pat. No. 6,761,416 of the author W. Moeny describe usage of multiple electrodes with high-voltage discharge in an aqueous environment, while removal of the crushed rock is performed by classical flushing.
An analogous method is described also in the U.S. Pat. No. 6,935,702 of the authors Okazaki et al. titled “Crushing Apparatus Electrode And Crushing Apparatus” with the usage of classical flushing.
The author A. F. Usov describes the use of electric discharge for drilling large diameters of over 1 m with the speed of up to several m/h, realized in the Scientific center Kola of Russian Academy of Sciences.
In the patent RU 2059436 C1 the author V. V. Maslov describes generating high voltage pulses for material destruction.
The authors Hirotoshi et al. describe in the paper Pulsed Electric Breakdown and Destruction of Granite, published in Jpn. J. Appl. Phys. Vol. 38 (1999) 6502-6505, successful usage of electric discharge on the typical geothermal rock-granite.
Rising of heavy undersea loads is described in the U.S. Pat. No. 4,422,801 titled “Buoyancy System For Large Scale Underwater Risers” of the authors Hale et al., where effective manipulations with large loads to over 3000 m depth are reached by variable buoyancy of ballast tanks.
In the U.S. Pat. No. 5,286,462 of the author J. Olson, there is described a system of quick gas generation for quick emptying ballast tanks for utilizing buoyancy for manipulating loads.
The problem of fast moving of an object in aqueous environment, which is a determining factor for transport effectiveness, is solved for military purposes in the U.S. Pat. No. 6,962,121 titled “Boiling Heat Transfer Torpedo” of the author R. Kuklinski and the U.S. Pat. No. 6,684,801 titled “Supercavitation Ventilation Control System”. These describe the method of artificial supercavitation, in which it is possible with a properly shaped object to achieve a speed of several hundred meters per second in water.
An apparatus for deep stimulating at the borehole bottom is described in the U.S. Pat. No. 4,254,828 titled “Apparatus For Producing Fractures And Gaps In Geological Formations For Utilizing The Heat Of The Earth” of the authors Sowa et al., in which the importance of pressure generation at the borehole bottom by an autonomous energy system is described. Similarly, also in the U.S. Pat. No. 7,017,681 of the authors Ivannikov et al. is described an autonomous system of stimulation by hydrodynamic effects at the borehole bottom.
At present, the state of techniques for forming casings is represented by expandable casings of various kinds. For example, technology described by the authors R. Cook et al. in the U.S. Pat. No. 6,739,392 titled “Forming A Wellbore Casing While Simultaneously Drilling A Bore” uses a sequence of steps, where special piping lowered down without casing is expanded by a pressure medium.
From the point of view of continuous casing production, the present state of the art provides a convenient starting point, because there have already been developed and put in practice cement composite mixtures, which quickly set under water and form high-strength concrete, especially for military purposes. Such cement composite mixtures have been developed also for storing hazardous wastes.
Substantial progress compared to the current state of the art is represented by a solution in which the system of interlocking pipes has been removed and is now replaced by freely moving containers in a water environment of continuously constructed casing. This is described below.
In the patent application 5087-2007 titled “Device For Excavation Of Deep Holes In A Geological Formation And Method Of Energy And Material Transport In These Holes” of the authors I. Koci{hacek over (s)} et al., there is described an innovative solution of a drilling device, wherein the main innovations are the transportation of rock, the material for casing production, and the transfer of energy through openings in the casing. The casing is filled with water by means of autonomous transport modules or containers by utilizing gas buoyancy. With negative buoyancy the containers move downwards. Casing is continuously formed from a part of the extracted rock and material supplied from the surface. The device includes an underground base, a transport module, a surface base, and the borehole in the geological formation and filled with water. Nevertheless, this device does not sufficiently solve the movement of transport modules, continuous preparation of the casing profile, manipulation with transport modules in the underground base and in the surface base, and control of and communication with the components. The device as a whole creates conditions for nearly linear dependence of the price of the created borehole (well) on its depth/length.
Summary of Recent Technologies
However, most of these methods have not reached the goal of substantial cost reduction in performing a deep drilling, as there have been several factors acting simultaneously against it:                problem of extracted material transport to the surface stayed unsolved without pipes connected in sequence one after the other,        problem of casing and its “in situ” formation,        problem of energy supply to the drilling device,        problem of energy demand, the necessity to disintegrate the whole borehole volume to small particles or even to melt down or evaporate the whole volume.        
Also the presence of a fluid (water, viscous transport fluid) in the borehole acts against the efficiency of these technologies. Energy supply has been solved, for example, by pressure water supply, electric energy supply via an electric cable, composite flushing line, or optical-fibre cables for high energy laser power supply. All mentioned technologies presume a certain steady, continually extended connection between the drilled ground and the surface. Similarly, also transport of the crushed rock still depends on the extending piping for transport media.
An equally important part of the borehole is the borehole wall casing made of gradually inserted pipes, which, moreover, narrow down with the borehole depth and so reduce the overall throughput and contribute to excessively rising price in dependence on the borehole depth. Recently, expandable casing with the same diameter in the whole borehole has been developed, but this only partially solves the problem of exponential price of the borehole.
None of the drilling technologies described so far has brought any innovation, which would substantially change the efficiency of the whole drilling process and the efficiency of the crushed rock transport to the surface, and which would guarantee drilling to large depths (over 5 km) and, simultaneously, guarantee approximately linear price dependence. From this, it follows the need of such technology, which substantially solves disadvantages of the current state of the art in the following aspects:                transport of energy downwards to the drilling process,        transport of the crushed rock to the surface so that direct continuous physical interconnection between the surface and the drilling device at the borehole bottom is disconnected in a way that is independent on the actual depth of the borehole,        process of casing formation would be performed continuously and in parallel with the process of borehole formation,        achievement of economical energy usage in crushing the rock and its transport to the surface,        possibility of cutting the rock into blocks and of their transport to the surface,        functionality of the device also at high pressures and temperatures in the borehole in the rock, with the borehole being flooded with fluid.        